Field of the Invention
The present disclosure relates generally to charge pump circuits and more specifically to switched-capacitor power electronic circuits.
Description of Related Art
In power conversion solutions, from DC to DC or AC to DC, switching capacitor architecture solutions are used. They consist of capacitors that are switched to move electrical charges from a voltage source such as a battery to an electric network or load.
Charge Pump Circuits: An Overview on Design Strategies and Topologies by Palumbo (2010), describes how charge pumps circuits are widely used in integrated circuits devoted to several kind of applications such as smart power, nonvolatile memories, switched capacitor circuits, operational amplifiers, voltage regulators, SRAMs, LCD drivers, piezoelectric actuators, RF antenna switch controllers, etc., due to the continuous power supply reduction.
Switched-Capacitor Power Electronic Circuits by Ioinovici (2002), describes the main orientations in power electronics in the last decade with the development of switching-mode converters without inductors and transformers. These converters are lightweight, small size and high power density as the result of using only switches and capacitors in the power stage. Thus, they serve as ideal power supplies for mobile electronic systems (e.g. cellular phones, personal digital assistants, and so forth). Switched-capacitor (SC) converters, with their large voltage conversion ratio, are a response to such challenges of the 21st century as high-efficiency converters with low EMI emissions and the ability to realize steep step-down of the voltage (to 3V or even a smaller supply voltage for integrated circuits) or steep step-up of the voltage for automotive industry or internet services in the telecom industry.
Most topologies of charge pumps are based on three types: Dickson, crossconnecting, and Makowski, as described in Analysis and Design of Makowski charge-pump cell by Liu (2005). They are composed of capacitors that are switching between different voltage levels (flying capacitors) and capacitors connected to the load (filtering capacitors). The flying capacitors are used to transfer the charge from the battery source to the load. Those architectures have typically two or more phases that are of two types, one used to recharge the flying capacitor, and the second to discharge the flying capacitor.
FIG. 1 shows a classical charge pump latest stage with switching capacitors Cn (flying) and Cf (filtering) of the related art. The Cn capacitors are part of the charge pump core that can be of different architectures. The Cf capacitors have always been required and act as an all time available energy reserve connected to the load. This ensures continuous current through the load during the Cn charging phases and during transitions. Typically one of the nodes of the Cn capacitor connected to the load in the last stage through one switch (S2), is also connected to the previous stage through another switch (S1), and it is important to avoid closing, and passing current in, both switches (S1&S2) at the same time. Switch S1 or S2 is most likely a MOS transistor driven with a signal from a driver circuit that turns on (closes the switch) and off (opens the switch) the device to operate it as a switch.
FIG. 2 illustrates Cn (flying) capacitor discharge and recharge phases with Tbbm (break before make) time of the related art. The discharge phase and charge phase are controlled independently and a minimum break-before-make time, between closing the first switch (S1) and opening the second switch (S2), is guaranteed by design.
FIG. 3 shows a circuit diagram of charge pumps of the related art. Interleaved structures have been proposed where two or more charge pumps (A&B) are working in parallel. This has the advantage to increase the output power and reduce the requirement on the Cf (filtering) capacitors, now delivering charge to the load only during Tbbm (break-before-make) time, instead of the full half-period.
FIG. 4 illustrates a signal diagram of CnA and CnB (flying) capacitor discharge and recharge phases with Tbbm (break-before-make) times, for two charge pumps working in parallel of the related art. The time that the load current is delivered only by the Cf (filtering) capacitors is now Tbbm, instead of the full half-period, which allows use of a smaller value for Cf.